1. Field of the Invention
This application relates to a dropout fuse assembly and to a fuse holder forming a part thereof whereby a repeater fuse characteristic may be imparted to an installation having conventional dropout fuse elements with the result that electrical continuity can be automatically restored in the event of at least a first fuse of the assembly blowing.
2. Description of the Related Art
Fuses may be used extensively in high voltage electrical networks, such as at distribution points, in order to protect electrical equipment in the network from damage caused by electrical surges through the system, generally occasioned by short-circuits (including those resulting from lightning strikes), and overloads. Although such a surge is often of a very temporary nature, such as may be caused by lightning, a fuse will nevertheless blow irrespective of whether the temporary surge is likely to repeat itself soon, if ever.
In the absence of a fuse holder assembly that can automatically connect sequentially to a second fuse, and possibly even a third fuse, one at a time, the consumers supplied through that particular circuit will be subjected to a power interruption that can be extremely inconvenient, harmful and costly. As a result of the fact that electrical distribution lines generally extend over long distances with poor vehicular access, it may take a considerable length of time to locate a fault and repair it. To make matters worse, such power interruptions often occur at night time, or in bad weather, or both. All this can contribute to extended periods of time for which the power supply remains interrupted.
In order to facilitate the location of a blown fuse, and its replacement, dropout fuse assemblies may be widely used in which instance a fuse wire that extends through a tubular fuse element is itself employed to hold an articulated link in an extended position. When the fuse wire blows, the tubular fuse element drops out of its operative position and hangs, typically upside down, from the articulated link thereby being highly visible and facilitating replacement. Elongate tools are available to enable such tubular fuse elements, at least in some instances, to be replaced by an electrician standing on the ground.
In order to combat the deleterious effects of downtime consequent on a temporary surge that is unlikely to be repeated, various so-called repeater fuses have been proposed, and used. Such repeater fuse assemblies usually have at least a second and possibly a third fuse element stored in the assembly with a mechanism triggered by the loss of tension in a fuse wire that blows so that another fuse is automatically connected into the relevant circuit by the mechanism.
Such repeater fuse assemblies are described, for example, in UK Patent Number GB 2299718; in U.S. Pat. No. 2,378,582; and in International Patent Application Number WO03/021619. Whilst these arrangements may operate effectively, they may be complicated, accordingly costly, and may not enable blown fuses to be replaced without interrupting the relevant power supply.
U.S. Pat. No. 2,211,974, on the other hand, does provide an arrangement in which a fuse can be replaced without interrupting the power supply but the fuse assembly is extremely complicated and, applicant believes, relatively costly.
These repeater fuse assemblies also suffer from the disadvantage that there is an inadequate time delay between the one fuse blowing and the other becoming connected to enable the arc created by the blown fuse to clear adequately.
In any event, each of these proposals requires replacement of the entire fuse assembly in order to implement them with the accompanying power interruptions and both direct and indirect costs. Still further, in at least one instance, installation into a network requires that the system be modified with accompanying necessary downtime.
It will be understood that the nature of a fuse with which certain embodiments are concerned is that the fuse itself generally forms part of the length of a fuse wire that passes through and insulating passage in a fuse element or holder and that both the fuse and fuse wire may typically be held in tension in the operative condition.